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The rocket is fired vertically and tracked by the radar station shown. When \(\theta\) reaches \(60^{\circ},\) other corresponding measurements give the values \(r=\) \(9 \mathrm{km}, \ddot{r}=21 \mathrm{m} / \mathrm{s}^{2},\) and \(\dot{\theta}=0.02 \mathrm{rad} / \mathrm{s} .\) Calculate the magnitudes of the velocity and acceleration of the rocket at this position.

Short Answer

Expert verified
The velocity is 180 m/s and the acceleration is 17.4 m/s².

Step by step solution

01

Understand the Problem

Consider that we're dealing with polar coordinates where the position of the rocket is represented by \(r\) (the radial distance from the radar station) and \(\theta\) (the angle of elevation from the horizontal). We need to find the velocity and acceleration magnitudes.
02

Polar Coordinates to Cartesian Equations

The velocity \(v\) in polar coordinates is given by the formula:\[ v = \sqrt{(\dot{r})^2 + (r \cdot \dot{\theta})^2} \]We need \(\dot{r}\), the radial velocity, which can be found by integrating \(\ddot{r}=21\) m/s² over time if initial conditions are known, or if additional information is provided.
03

Calculate Radial and Angular Components

Given \(r = 9\) km (or 9000 meters), \(\dot{\theta} = 0.02\) rad/s, and \(\ddot{r} = 21\) m/s²:_First,_ convert \(r\) to meters: \(r = 9000\) m.There is no information about explicit \(\dot{r}\), assuming it starts from rest or is 0 due to lack of data.The angular velocity component is \(r\dot{\theta} = 9000 \times 0.02 = 180\) m/s.
04

Compute Magnitude of Velocity

Assuming initial \(\dot{r} = 0\):The magnitude of velocity, \(v\), is given by:\[ v = \sqrt{0^2 + (180)^2} = 180\] m/s.This is only valid under the assumption \(\dot{r} = 0\), without initial conditions given.
05

Find Radial and Tangential Components of Acceleration

In polar coordinates, acceleration \(a\) has two components:- Radial: \(a_r = \ddot{r} - r \cdot (\dot{\theta})^2\)- Transverse (angular): \(a_t = r \cdot \ddot{\theta} + 2 \cdot \dot{r} \cdot \dot{\theta}\)Calculate the radial component:\(a_r = 21 - 9000 \times (0.02)^2 = 21 - 3.6 = 17.4\) m/s².For the transverse component:Given \(\dot{r} = 0\),\(a_t = 9000 \cdot 0 + 0 = 0\) m/s².
06

Calculate Magnitude of Acceleration

Magnitude of acceleration is calculated by:\[ a = \sqrt{a_r^2 + a_t^2} = \sqrt{(17.4)^2 + 0^2} = 17.4 \] m/s².

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Rocket Motion
Rockets often take a unique path, combining both linear and rotational movement. When observing a rocket's trajectory, we often rely on radar systems that apply polar coordinates to track its position. This method involves measuring the straight distance from a fixed origin, known as the radial distance, and the angle from a fixed direction, termed as the angular measurement. Understanding rocket motion involves comprehending these simultaneously changing quantities. This not only positions the rocket in space but also describes its dynamic flight characteristics.
In the given problem, the radar tracks the rocket as it ascends, capturing essential data including the distance and the angle to ascertain the rocket's instantaneous motion attributes. By combining these measurements, one can derive information such as speed and acceleration, which are crucial for ensuring a successful mission.
Velocity Calculation
Calculating the velocity of a rocket in polar coordinates involves two primary components: the radial velocity and the angular velocity. Radial velocity is essentially the change in position over time concerning the radial distance, denoted \(\dot{r}\). Angular velocity refers to how fast the angle \(\theta\) changes, represented as \(\dot{\theta}\).
The formula to determine the total velocity \(v\) of the rocket at any moment is:
\[ v = \sqrt{(\dot{r})^2 + (r \cdot \dot{\theta})^2} \]
Here, any motion outward or inward along the radial path is captured by \(\dot{r}\), while the circular motion around the origin is described by \(r \cdot \dot{\theta}\). In scenarios where explicit \(\dot{r}\) isn't given, like in our problem, assumptions or additional data can aid in solving for this neglectable value, focusing on angular contributions like \(r \cdot \dot{\theta}\) instead.
Acceleration Computation
Acceleration in polar coordinates is more complex as it features two distinct components: radial and angular acceleration. Radial acceleration \(a_r\) deals with changes along the line joining the rocket and the radar. Angular, or transverse acceleration \(a_t\), handles changes perpendicular to this radial line.
To compute these components, use the following formulas:
  • Radial component: \(a_r = \ddot{r} - r \cdot (\dot{\theta})^2\)
  • Angular component: \(a_t = r \cdot \ddot{\theta} + 2 \cdot \dot{r} \cdot \dot{\theta}\)
These equations capture how a rocket accelerates by accounting for both outward radial motion and lateral movements. In the given exercise, an assumption that \(\dot{r} = 0\) results in a simplified computation, but thorough data would consider minute factors influencing these velocity changes.
Radial and Angular Components
In polar coordinates, understanding the radial and angular components is critical for analyzing the motion of objects like rockets. The radial component refers to anything that directly affects or arises from the direction radially outward or inward from the origin point, while the angular component concerns itself with rotational or side-to-side motion around the origin.
In practical terms, the radial component (denoted \(r\)) deals with changes in distance from a point, key for calculating radial velocity and acceleration. On the other hand, the angular component (denoted \(\theta\)) reflects how something is rotating about a point and contributes to angular velocity and angular acceleration.
  • Radial components often influence speed significantly when the object moves along a straight path.
  • Angular components become crucial when an object is orbiting or rotating, providing insights into its circular dynamics.
By breaking down rocket motion into these components, engineers can maximize efficiency and predictability in aerospace designs.

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